Petroleum refining and petrochemical processes include reaction zones that contain catalysts used to promote various chemical reactions. For example, hydrocracking, hydro-treating, naphtha reforming, naphtha isomerization are all process that use catalysts to promote the different chemical reactions associated therewith. These catalysts comprise, among other compounds, metals, typically noble or precious metals.
When the catalysts are spent, they may be processed to recover the noble metals. Since the metals are expensive, the loss of even a small amount of catalyst metal can be costly for a refiner. Therefore, refiners desire to maximize the recovery of the catalyst metals to minimize any losses.
The catalyst pellets are typically contained in one or more beds within the reaction zone. During the loading and the handling of these beds, catalyst fines are typically generated. Once the reactor is brought back on line, the catalyst fines migrate through the reaction zone and are carried out with the liquid flowing through the reactor. Not only does this result in a loss of catalyst fines, it can result in a loss of processing fluid, if the startup fluid is the fluid to be processed. Additional catalyst fines can be generated merely by the operation of the reaction zone. These catalyst fines can be carried along with the liquid effluent and lost into downstream equipment. Thus, any catalyst metal lost during operation as a result of catalyst fines generation will lower metals recovery and increase the capital loss for the refiner.
It is known to recover catalyst in various Fisher-Tropsch reactions in which the synthesis catalyst particles are in a slurry or processing fluid. For example, U.S. Pat. Pub. No. 2013/0144099 discloses the use of filters to capture the synthesis catalyst particles and separate same from the hydrocarbon oil. Another process for filtering an effluent stream from a Fisher-Tropsch reactor is disclosed in U.S. Pat. No. 8,344,199. The process disclosed in U.S. Pat. No. 8,344,199 uses two filter sections to avoid a pressure drop associated with filtering the effluent stream. However, in both of these references, various filters are separated, thus creating problems associated with changing the filters when they become saturated. Thus, it is believed that these processes fail to fully address minimizing downtime for a reactor. Furthermore, while presumably effective for their intended uses, these processes are not believed to be readily suited to recover catalyst fines from an effluent from a fixed bed reactor.
As mentioned above, catalyst fines are especially a problem during start-up periods for the fixed bed reactors after the beds have been re-loaded with new catalyst. Accordingly, during the start-up of the reactor, there will be an initial surge of catalyst fines in the liquid passing through the reactor. Typically, to avoid a pressure drop downstream created by the catalyst fines, the start-up liquid (or flush liquid) is used as a “once through” liquid. Once the liquid is substantially void of catalyst fines and any other impurities, the reaction process can be started.
One drawback with such a process is the loss of the reactor being online. Indeed, it can take between four to eight hours before the flush liquid is substantially free from catalyst fines. However, and more importantly, the flush liquid that is used is typically the processing stream. While the “once through” fluid can be recovered and used in other, less desirable processes, it would be more beneficial for a refiner to be able to recycle the flush liquid (which comprises the processing stream) back to the reactor.
Therefore, there is a need for an effective and efficient process to recover the catalyst fines from a liquid stream from a fixed bed reaction zone.
Additionally, there is a need for such a filtering process that can minimize, if not, eliminate any downtime for the reaction zone associated with the filtering process.